[Laser] discrete vs op amp sensitivity

[Art]

Hi Glenn,

Absolutely correct although we use a simpler 'formula', which is 
simply that each additional sampling bit increases the dynamic range 
by 6 db. The end result is the same however, whether you use the 
formula or the simplified 6 db per bit method.

48 db is an ENORMOUS improvement, allowing one to continue receiving 
useful data even though there are strong interfering signals within 
the passband of the sound card.

In the lab, you probably don't need the extra bits as there probably 
aren't large amplitude interfering signals on your workbench setup. 
In the real world however, large interfering signals are everywhere 
and can appear and disappear without notice or warning::>

Creative Labs used to sell a 24 bit sound card that had so much noise 
associated with it that it performed no better than a 16 bit sound 
card (because the first 6 bits did nothing but digitize the self made 
noise). There was a very large class action suit over this and 
Creative Labs lost. I think they had to refund or give credit to 
anyone who bought one of these and noticed poor performance.

My eyes began to open when I learned of this issue. The very 
expensive electronics associated with a high end sound card can 
effectively negate the extra resolution available IF the sound card 
input circuit generates noise. Dynamic range is very important, even 
in laser reception::> When one chooses a sound card for a serious 
laser receiver, the usable dynamic range and the noise generated by 
the sound card are issues that need to be considered.

Regards,

Art



At 01:09 AM 1/16/2007, you wrote:
>Hi all!
>
>I took a moment to quantify the difference between the dynamic range 
>of a 16 bit sample and a 24 bit sample. Since the sample is a 
>voltage measurement, the dynamic range is expressed in dBv. A little 
>thought will show that the dynamic range is from one bit to the 
>level associated with however many bits the sample has, thus the 
>dynamic range of an n-bit sample is:
>
>    20* log10(2**n).
>
>Thus a 16 bit sample (standard music CD) has a dynamic range of 96 
>dBv and a 24 bit sample has a dynamic range of 144 dBv. A 24 bit 
>sample has 48 dBv more dynamic range than a 16 bit sample.
>
>73 de Glenn wb6w
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